package com.yea.core.util;

/**
 * 复制自Shiro
 * @author yiyongfei
 *
 */
public class HexUtil {

    /**
     * Used to build output as Hex
     */
    private static final char[] DIGITS = {
            '0', '1', '2', '3', '4', '5', '6', '7',
            '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'
    };

	/**
	 * Encodes the specifed byte array to a character array and then returns
	 * that character array as a String.
	 *
	 * @param bytes
	 *            the byte array to Hex-encode.
	 * @return A String representation of the resultant hex-encoded char array.
	 */
	public static String encodeToString(byte[] bytes) {
		char[] encodedChars = encode(bytes);
		return new String(encodedChars);
	}

	/**
	 * Converts an array of bytes into an array of characters representing the
	 * hexidecimal values of each byte in order. The returned array will be
	 * double the length of the passed array, as it takes two characters to
	 * represent any given byte.
	 *
	 * @param data
	 *            byte[] to convert to Hex characters
	 * @return A char[] containing hexidecimal characters
	 */
	public static char[] encode(byte[] data) {
		int l = data.length;
		char[] out = new char[l << 1];
		for (int i = 0, j = 0; i < l; i++) {
			out[j++] = DIGITS[(0xF0 & data[i]) >>> 4];
			out[j++] = DIGITS[0x0F & data[i]];
		}
		return out;
	}

	/**
	 * Converts the specified Hex-encoded String into a raw byte array. This is
	 * a convenience method that merely delegates to {@link #decode(char[])}
	 * using the argument's hex.toCharArray() value.
	 *
	 * @param hex
	 *            a Hex-encoded String.
	 * @return A byte array containing binary data decoded from the supplied
	 *         String's char array.
	 */
	public static byte[] decode(String hex) {
		return decode(hex.toCharArray());
	}

	/**
	 * Converts an array of characters representing hexidecimal values into an
	 * array of bytes of those same values. The returned array will be half the
	 * length of the passed array, as it takes two characters to represent any
	 * given byte. An exception is thrown if the passed char array has an odd
	 * number of elements.
	 *
	 * @param data
	 *            An array of characters containing hexidecimal digits
	 * @return A byte array containing binary data decoded from the supplied
	 *         char array.
	 * @throws IllegalArgumentException
	 *             if an odd number or illegal of characters is supplied
	 */
	public static byte[] decode(char[] data) throws IllegalArgumentException {
		int len = data.length;
		if ((len & 0x01) != 0) {
			throw new IllegalArgumentException("Odd number of characters.");
		}
		byte[] out = new byte[len >> 1];
		for (int i = 0, j = 0; j < len; i++) {
			int f = toDigit(data[j], j) << 4;
			j++;
			f = f | toDigit(data[j], j);
			j++;
			out[i] = (byte) (f & 0xFF);
		}
		return out;
	}

	/**
	 * Converts a hexadecimal character to an integer.
	 *
	 * @param ch
	 *            A character to convert to an integer digit
	 * @param index
	 *            The index of the character in the source
	 * @return An integer
	 * @throws IllegalArgumentException
	 *             if ch is an illegal hex character
	 */
	protected static int toDigit(char ch, int index) throws IllegalArgumentException {
		int digit = Character.digit(ch, 16);
		if (digit == -1) {
			throw new IllegalArgumentException("Illegal hexadecimal charcter " + ch + " at index " + index);
		}
		return digit;
	}

}
